"COMBUSTION CHAMBER FOR AN INTERNAL COMBUSTION ENGINE"

Abstract

A combustion chamber structure for an internal combustion engine having a hemispherical combustion chamber (6) defined by an inner surface of a cylinder head (4) and a crown of a piston (5), and an electrode (12a) of a spark plug (12) fitted into the cylinder head (4) caused to face into the combustion chamber (6) close to a peripheral edge section of the combustion chamber (6), characterized in that a squish area (17) is provided between a peripheral edge section of a ceiling surface of the combustion chamber (6) and a peripheral edge section of the crown of the piston (5), and squish flow (F) of fuel-air mixture erupting from an area (17f) of the squish area (17) furthest away from the electrode (12a) of the sparkplug (12) is directed towards the electrode (12a), while squish flow (N) of fuel-air mixture erupting from an area (17n) of the squish area (17) closest to the electrode (12a) is directed below the electrode

Full Text

The present invention relates to a combustion chamber at structure for an internal combustion engine.
The present invention relates to a combustion chamber structure for an internal combustion engine having a combustion chamber defined by an inner surface of a cylinder head and a crown of a piston, and an electrode of a spark plug fitted into the cylinder head caused to face into the combustion chamber close to a peripheral edge section the combustion chamber.
[Related Art]
A combustion chamber structure for an internal combustion engine is well known, as disclosed, for example, in Japanese Patent Publication No. Sho. 58-43565.
[Problems To Be Solved By The Invention]
In an internal combustion engine, in order to stop knocking, a spark plug electrode is arranged in the middle of the combustion chamber to make the flame propagation distance as small as possible, and this is generally effective. However, depending on the structure or shape of the combustion chamber, it is sometimes difficult to appropriately arrange the spark plug in such a way because of the relationship of the arrangement of the inlet and exhaust valves etc., that is, the spark plug electrode is inevitably arranged close to a peripheral edge portion of the combustion chamber. In such a case, since the flame propagation distance inevitably becomes long, it is likely that knocking caused by autoignition of end gases will occur.
The present invention was conceived to solve the above described problem, and has as its object to provide a combustion chamber for an internal combustion engine that can bring about improved resistance to knocking by completing normal flame propagation before end gases reach the point of autoignition, even if a spark plug electrode is arranged close to a peripheral edge section of the combustion chamber.
Accordingly, there is provided a combustion chamber jjtrjuetofe for an internal combustion engine having a hemispherical combustion chamber defined by an inner surface of a cylinder head and a crown of a piston, and an electrode of a spark plug fitted into the cylinder head caused to face into the combustion chamber close to a peripheral edge section of the combustion chamber, characterized in that
a squish area is provided between a peripheral edge section of a ceiling surface of the combustion chamber and a peripheral edge section of the crown of the piston, and
squish flow of fuel-air mixture erupting from an area of the squish area furthest away from the electrode of the sparkplug is directed towards the electrode, while squish flow of fuel-air mixture erupting from an area of the squish area closest to the electrode is directed below the electrode.
According to the first aspect, during the compression stroke, if the piston approaches top dead center, a squish flow of fuel-air mixture towards the electrode of the spark plug gushes out from an area on the edge of the combustion chamber furthest away from the electrode. As a result, end gas pressure increase caused by the flame is delayed by this squish flow colliding with the outer surface of a flame generated by the spark of
the spark plug. Therefore, before the end gas autoignites, the flame propagates normally to the furthest edge of the combustion chamber and normal combustion with no knocking takes place.
Also, because squish flow from a section closest to the electrode is not directed to the electrode, but strays below it, it is possible to promote propagation and prevent the occurrence of knocking while avoiding blowing out the remaining flame that is possible immediately after sparking of the electrode, and swirling the fuel-air mixture.
Since the electrode of the spark plug is arranged close to a peripheral edge of the combustion chamber, it occupies a comparatively low position in the combustion chamber. A squish area is provided between a peripheral edge section of a ceiling surface of the combustion chamber and a peripheral edge section of the crown of the piston, in such a manner that a squish flow of fuel-air mixture spurting out of the area furthest away from the electrode is directed towards the electrode while a squish flow of fuel-air mixture spurting from an area closest to the electrode is directed below the electrode, a sloping surface formed from the peripheral edge section of the crown of the piston inevitably becomes slightly sloped. As a result, piston durability is ensured and improved knocking resistance is realized by the fact that increase in heat receiving surface area of the piston tope face accompanying the formation of this sloped surface is extremely slight and the total squish flow flows close to the piston crown to effectively cool the piston crown.
A second aspect of the present invention, in addition to the first aspect, has heads of each of an inlet valve and an exhaust valve arranged close to each other on the ceiling surface of the combustion chamber, and the electrode of the spark plug arranged close to an edge section of the combustion chamber on one side of a plane including the two axes of the inlet valve and the exhaust valve.
According to the second aspect, it is possible to enlarge the diameter of the intake port and the exhaust port without interfering with the sparkplug, and it is possible to lower the exhaust resistance accompanying increase in charging efficiency, improve knock resistance and improve engine output.
[Embodiments of the Invention]
Embodiments of the present invention will be described in the following with reference to the attached drawings.
[Brief description of the Drawings]
Fig 1 is a lateral cross sectional drawing of an internal combustion engine provided with the combustion chamber structure of the present invention; Fig. 2 is a cross sectional drawing along line 2 - 2 in Fig. 1; Fig. 3 is a cross sectional drawing along line 3 - 3 ifi Fig. 1; Fig. 4 is a cross sectional drawing along line 4 - 4 in Fig. 1;
Fig. 5 is an explanatory drawing showing the combustion state of a fuel-air mixture in the combustion chamber;
Fig. 6 is a cross sectional drawing, corresponding to Fig. 1, showing a combustion chamber structure of a comparative example; and
Fig. 7 is a graph showing comparison of knock resistance for the present invention and the comparative example.
Fig. 1 is a longitudinal cross sectional drawing of an internal combustion engine provided with the combustion chamber structure of the present invention, Fig. 2 is a cross sectional drawing along line 2 - 2 in Fig. 1, Fig. 3 is a cross sectional drawing along line 3 -3 in Fig. 1, Fig. 4 is a cross sectional drawing along line 4 - 4 in Fig. 1, Fig. 5 is an explanatory drawing showing the combustion state of a fuel-air mixture in the combustion chamber, Fig. 6 is a cross sectional drawing, corresponding to Fig. 1, showing a combustion chamber structure of a comparative example, and Fig. 7 is a graph showing comparison of knock resistance for the present invention and the comparative example.
in Fig. 1 and Fig. 2, an internal combustion engine 1 is provided with a cylinder block 2, a cylinder head 4 joined to the upper surface of the cylinder block 2 with a gasket 3 interposed between them, and a piston 5 fitted inside a cylinder bore 2a formed in a central portion of the cylinder block 2 so as to move up and down. A combustion chamber 6 is defined between the inner surfaces of the cylinder head 4 and the crown of the piston 5.
The intake port 7 and the exhaust port 8 open into a hemispherical ceiling surface of the combustion chamber 6, and a poppet type inlet valve 10 and exhaust valve 11 for opening and closing these ports are housed in the cylinder head 4. The heads 10a and 1 la of each valve 10 and 11 have as large a diameter as possible so that each of the inlet port 7 and the exhaust port 8 are arranged close to each other.
The electrode 12 a of the spark plug screwed in to the cylinder head 4 is arranged close to the edge of the combustion chamber 6 so as to avoid each of the heads of the inlet valve 10 and exhaust valve 11 and face into the combustion chamber 6. That is, the electrode 12a is arranged on one side of the plane A including the axes O1 and O2 of the inlet valve 10 and the exhaust valve 11, close to the edge of the combustion chamber 6.
The inlet valve 10 and the exhaust valve 11 are opened and closed by well known valve gear 13 driven by a crank shaft (not shown).
As shown in Fig. 1 to Fig. 4, an upper truncated cone-shaped surface 15 sloping upwards towards the center of the combustion chamber is formed in the ceiling surface of the combustion chamber 6, while a lower truncated cone-shaped surface 16 having the same angle of gradient as the upper surface 15 is formed on the edge of the crown of the
piston 5. These upper and lower sloped surfaces 15 and 16 form an annular squish area 17 for sweeping a squish flow of fuel-air mixture from the two surfaces 15 and 16 when the piston 5 reaches top dead center, and the gradient of the two surfaces 15 and 16 is set so that squish flow F from the region 17f of the squish area 17 furthest away from the electrode 12a is directed towards the electrode 12a, while squish flow N from the region 17n of the squish area 17 closet to the electrode 12a is directed downwards to avoid the electrode 12a.
Next, the operation of this embodiment will be described.
With the piston 5 at the intake cycle, a fuel-air mixture is inducted from the intake port 7 to the combustion chamber 6 by opening of the inlet valve 10, and this fuel-air mixture is compressed in the next compression cycle of the piston 5. However, when the piston 5 approaches top dead center the upper truncated cone shaped surface 15 at the edge of the ceiling surface of the combustion chamber 6 and the lower truncated cone shaped surface 16 of the crown of the piston 5 become close to each other to form the annular squish area 17. This means that fuel-air mixture begins to spurt from the squish area 17, and this spurt continues until the piston 5 is just past top dead center.
At this time, the squish flow F gushing from the region 17f furthest from the electrode 12a of the spark plug 12 is directed straight on towards the electrode 12a, but the squish flow N gushing from the region 17n closet to the electrode 12a is directed below the electrode 12a and misses it.
On the other hand, the spark plug 12 fires when the piston 5 arrives at a fixed position before top dead center and a flame 18 generated by ignition of the fuel-air mixture advances outward with the electrode 12a as its center, as shown in Fig. 5.
At this time, generally, the above described flame 18 reaches the area of the combustion chamber 6 close to the electrode 12a in a short time, and so it is unlikely that autoignition of end gases will occur in that region. However, because a suitable time is needed for the flame 18 to reach the region furthest away from the electrode 12a, end gases are pressurized by the wave front during that time, pre-flame reactions advance and autoignition arises. The resultant abnormal combustion is the cause of knocking.
However, with the present invention, the annular squish area 17 formed at the
edge of the combustion chamber 6 has a squish flow of fuel-air mixture F from the region far away from the electrode 12a that is directed directly towards the electrode 12a, as described above, which means that pressurization of end gasses by the flame 18 is avoided by virtue of the fact that this squish flow F collides vertically with the outer surface of the flame 18. Thus, before autoignition of the end gases the flame 18 propagates normally to the furthest edge of the combustion chamber 6 and it becomes possible to achieve normal combustion free from knocking.
Also, with respect to the squish area 17, a squish flow N gushing from the region 17n closest to the electrode 12a is not directed to the electrode 12a, but goes below it and misses it, which means that blowing out of a flame immediately after sparking of the electrode 12a is avoided while the flame 18 is conveyed rap idly by swirling the fuel-air mixture, which also helps prevent knocking from occurring.
Because the electrode 12a of the spark plug 12 is arranged close to the edge of the combustion chamber 6, it occupies a comparatively low position in the combustion chamber 6, and by providing the squish area 17 between the edge part of the ceiling surface of the combustion chamber 6 and the edge of the crown of the piston 5 such that a fuel-air mixture squish flow F from a region 17f furthest from the electrode 12a is directed towards the electrode 12a while a fuel-air mixture squish flow N from a region 17n closest to the electrode is directed below the electrode 12a, a sloping surface formed at the edge of the crown of the piston 5 inevitably has a small slope angle 9 (refer to Fig. 5). This in
turn means that increase in heat receiving surface area of the crown of the piston 5 accompanying the formation of the sloping surface is extremely small, and the total of the squish flows F and N flow close to the crown of the piston 5 effectively cooling the crown of the piston 5, which contributes to improvement in knocking resistance and ensuring durability of the piston 5.
With the combustion chamber structure of the comparative example shown in Fig. 6, a squish area 17' is formed between an annular horizontal surface 15' at the edge of the ceiling surface of the combustion chamber 6 and an annular horizontal surface 16' at the edge of the crown of the piston 5. The rest of the structure is the same as in the above described embodiment of the present invention, and in the drawing, parts corresponding to those in the embodiment will be assigned the same reference numerals.
In this comparative example, squish flow of fuel-air mixture from the squish area
17' is stirred in with the fuel-air mixture at a section of the combustion chamber below electrode 12a.
If respective knocking tests for the combustion chamber arrangement of the present invention and the combustion chamber arrangement of the comparative example are carried out and compared, the results shown in Fig. 7 are obtained.
As test conditions, the squish gap of both combustion chamber structures was 0.8 mm, compression ratio was 9.2, lubricating oil temperature was 125 - 145°C, spark plug temperature was 204 - 282°C, and throttle opening amount was fully open.
As the test method, internal pressure of the cylinder bore 2a was detected using a Kisler acupressure sensor, ignition timing was advanced while monitoring on an oscilloscope, and the point in time at which high frequencies that cause knocking started to appear was determined as the knocking start ignition timing.
As is clear from Fig. 7, the knocking start ignition timing for the present invention is judged to be delayed by a crank angle of angle of 5 - 10°Ccompared to the knocking start timing of the comparative example, which confirms that the knocking resistance of the combustion chamber arrangement of the present invention is improved.
With the combustion chamber arrangement of the present invention, the heads lOa and 1 la of each inlet valve 10 and exhaust valve 11 are arranged close to each other in the ceiling surface of the combustion chamber 6, and the electrode 12a of the spark plug 12 is arranged on one side of a plane A including both of the axes of the inlet valve 10 and exhaust valve 11, which means that the inlet port 7 and exhaust port can be increased in diameter without causing any interference with the spark plug 12, filling efficiency can be increased while exhaust resistance is lowered, it is possible to improve the knocking resistance and the output of the engine can be improved.
The present invention is not limited to the above described embodiment, but various design changes are possible without departing from the spirit and scope of the invention. For example, it is possible to remove that part of the squish area 17 that would interfere with the heads10a and 1 la of the inlet valve and exhaust valve if the heads of the inlet valve and exhaust valve 11 are further increased in diameter. Also, instead of having a hollow shape as shown in the drawings, a section of the crown of the piston 5 that
surrounds the squish area 17 can also have a gently swelling shape.
[Effects of the Invention]
According to a first aspect of the invention as described above, in an internal combustion engine having a combustion chamber defined by an inner surface of a cylinder head and a crown of a piston, and an electrode of a spark plug fitted into the cylinder head caused to face into the combustion chamber close to a peripheral edge section the combustion chamber, a squish area is provided between a peripheral edge section of a ceiling surface of the combustion chamber and a peripheral edge section of the crown of the piston, and squish flow of fuel-air mixture erupting from an area of the squish area furthest away from the electrode of the spark plug (12) is directed towards the electrode, while squish flow of fuel-air mixture erupting from an area of the squish area closest to the electrode is directed below the electrode. This means that turbulence is caused in the fuel-air mixture without blowing out a flame immediately after firing of the electrode and the flame propagation is promoted, due to the fact that a squish flow from a region of the edge of the combustion chamber far away from the electrode presses the outer surface of a flame generated from the electrode and brings about a delay in the compression of the end gases by the flame, while a squish flow from a region of the combustion chamber close to the electrode avoids the electrode, with the result that it is possible to greatly improve the knocking resistance. Also, the electrode of the sparkplug is arranged close to the edge of the combustion chamber, which means that it occupies a comparatively low position in the combustion chamber, and by providing the squish area between the edge part of the ceiling surface of the combustion chamber and the edge of the crown of the piston such that a fuel-air mixture squish flow from a region furthest from the electrode is directed towards the electrode while a fuel-air mixture squish flow from a region closest to the electrode is directed below the electrode, a sloping surface formed at the edge of the crown of the piston inevitably becomes slightly inclined which in turn means that increase in the heat receiving surface area of the crown of the piston accompany ing the formation of the sloping surface is extremely small, and the total squish flow close to the crown of the piston effectively cools the crown of the piston, making it possible to improve knocking resistance and ensure durability of the piston.
According to the second aspect of the present invention, the heads of each inlet valve and exhaust valve are arranged close to each other in the ceiling surface of the combustion chamber, and the electrode of the spark plug is arranged on one side of a plane including both of the axes of the inlet valve and exhaust valve, which means that nothing
interferes with the spark plug, and the irdet port and exhaust port can be increased in diameter, charging efficiency can be increased while exhaust resistance is lowered, it is possible to improve the knocking resistance and the output of the engine can be improved.
[Description of the Numerals]
1 internal combustion engine
4 cylinder head
5 piston
6 combustion chamber
10 inlet valve
10a inlet valve head
11 exhaust valve
I1 a exiiaust valve head
12 spark plug
12a spark plug electrode
17 squish area
17f area of squish region far from electrode
17n area of squish region near to electrode
A plane
01 inlet valve axis
02 exhaust valve axis
F squish flow erupting from area far from electrode
N squish flow erupting from area near to electrode
Translation for the Drawings
Fig. 7
Engine Speed (rpm) Knocking start ignition timing Present invention Comparative example

CLAIM :
1. A combustion chamber Structure For an internal combustion engine having a hemispherical combustion chamber (6) defined by an inner surface of a cylinder head (4) and a crown of a piston (5), and an electrode (12a) of a spark plug (12) fitted into the cylinder head (4) caused to face into the combustion chamber (6) close to a peripheral edge section of the combustion chamber (6), characterized in that
a squish area (17) is provided between a peripheral edge section of a ceiling surface of the combustion chamber (6) and a peripheral edge section of the crown of the piston (5), and
squish flow (F) of fuel-air mixture erupting from an area (17f) of the squish area (17) furthest away from the electrode (12a) of the sparkplug (12) is directed towards the electrode (12a), while squish flow (N) of fuel-air mixture erupting from an area (17n) of the squish area (17) closest to the electrode (12a) is directed below the electrode (12a).
2. The combustion chamber structure for an internal combustion engine as claimed in claim 1, wherein heads (10a and 11 a) of each of an inlet valve (10) and an exhaust valve (11) are arranged close to each other on the ceiling surface of the
combustion chamber (6), and the electrode (12a) of the spark plug (12) is arranged close to an edge section of the combustion chamber (6) on one side of a plane (A) including the two axes (Oi and 62) of the inlet valve (10) and the exhaust valve (11).
3. A combustion chamber structure substantially as hereinbefore described with reference to an illustrated in the accompanying drawings.